Gas Detection Device and Control Method for Gas Detection Device

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2024-046031, filed on Mar. 22, 2024; the entire contents of which are incorporated herein by reference.

Embodiments described herein relate generally to a gas detection device and a control method for gas detection device

For example, there is a gas detection device that detects a detection target based on laser absorption by the detection target. Downsizing of gas detection devices is desired.

According to one embodiment, a gas detection device includes a driver section, an element section, a sensor, and a detector. The driver section includes a first driver and a second driver. The element section includes a first laser and a second laser. The first laser is configured to be driven by the first driver to emit a first beam. A first wavelength of the first beam is configured to change at a first frequency. The second laser is configured to be driven by the second driver to emit a second beam. A second wavelength of the second beam is configured to change at a second frequency. The second frequency is different from the first frequency. The second wavelength is different from the first wavelength. The sensor is configured to detect a received beam based on the first beam and the second beam. The detector configured to extract a target frequency component from an output signal from the sensor.

Various embodiments are described below with reference to the accompanying drawings.

The drawings are schematic and conceptual; and the relationships between the thickness and width of portions, the proportions of sizes among portions, etc., are not necessarily the same as the actual values. The dimensions and proportions may be illustrated differently among drawings, even for identical portions.

In the specification and drawings, components similar to those described previously or illustrated in an antecedent drawing are marked with like reference numerals, and a detailed description is omitted as appropriate.

is a schematic diagram illustrating a gas detection device according to a first embodiment.

As shown in, a gas detection deviceaccording to the embodiment includes a driver section, an element section, a sensor, and a detector.

The driver sectionincludes a first driverand a second driver. As described later, the driver sectionmay further include other drivers (for example, a third driverand a fourth driver).

The element sectionincludes a first laserand a second laser. As described later, the element sectionmay further include other lasers (for example, a third laserand a fourth laser).

The first laseris configured to be driven by the first driverand emit a first beam B. A wavelength of the first beam B(first wavelength) changes at a first frequency f. For example, a first drive signal Sdis supplied from the first driverto the first laser. The first wavelength is modulated by the first drive signal Sd.

The second laseris configured to be driven by the second driverand emit a second beam B. A wavelength of the second beam B(second wavelength) changes at a second frequency f. For example, the second drive signal Sdis supplied from the second driverto the second laser. The second wavelength is modulated by the second drive signal Sd. The second frequency fis different from the first frequency f. The second wavelength (wavelength band) is different from the first wavelength (wavelength band).

The sensordetects a received beam Rbased on the first beam Band the second beam B. The sensoroutputs an output signal Soaccording to the received beam R. The detectoris configured to extract a target frequency component from an output signal Sofrom the sensor.

In the example shown in, the first beam Band the second beam Bpass through the space SPon the path of the first beam Band the second beam B. In this example, these beams are reflected by the reflectorand reach the sensoras the received beam R. A detection targetexists in space

SP. The detection targetmay be, for example, gas. The detection targetincludes molecules or elements such as methane, dinitrogen monoxide, and carbon dioxide. The detection targethas a unique absorption wavelength. By evaluating the intensity of the received beam Rdetected by the sensor, the presence or absence of the detection targetand/or the concentration of the detection targetcan be detected. The detection targetmay include a plurality of substances of different types (a first detection target, a second detection target, etc.).

In the embodiment, the beam emitted by the laser is modulated at a particular frequency. A frequency component corresponding to the modulation frequency is extracted by the detector, and the intensity of the extracted signal is detected. In the embodiment, a plurality of laser beams (first beam B, second beam B, etc.) having mutually different wavelengths are detected by one sensor. The received beam Rreceived by the sensorincludes different wavelength components. The output signal Socorresponding to the received beam Ris extracted by the detectoras the target frequency component.

Thereby, a plurality of types of detection targetscan be detected with high accuracy by the single sensor.

For example, a reference example may be considered in which a first sensor is provided corresponding to the first laserand a second sensor is provided corresponding to the second laser. In this reference example, the number of sensors increases. Thereby, there is a limit to downsizing the device.

In contrast, in the embodiment, the single sensoris provided for a plurality of lasers that emit beams of different wavelengths. The number of sensorsmay be one. According to the embodiment, it is possible to provide a gas detection device that can be downsized. According to the embodiment, costs can be reduced. According to the embodiment, it is possible to provide a gas detection device that can reduce power consumption.

The first wavelength of the first beam Bis modulated at the first frequency faround a first intermediate wavelength. For example, the first wavelength changes between a first short wavelength and a first long wavelength at the first frequency f. The first long wavelength is longer than the first short wavelength. The first intermediate wavelength exists between the first long wavelength and the first short wavelength. For example, the first intermediate wavelength corresponds to absorption the wavelength of the first detection target(first substance). The intensity of the first intermediate wavelength changes depending on the presence or absence of the first detection target. The wavelength of the first beam Bto be modulated becomes the first intermediate wavelength twice during one period. Information regarding the presence or absence (and concentration) of the first detection targetcan be obtained by detecting a change in the frequency component twice the first frequency f. Based on this information, the first detection targetcan be detected.

For example, a first intensity of the output signal Soin a first state is lower than a second intensity of the output signal Soin a second state. A concentration of the first detection target(first gas, etc.) existing on the path of the first beam Bin the first state is higher than a second concentration of the first detection targetexisting on the path in the second state. The first state is a high concentration state. The second state is a low concentration state (or non-existent state). In such a case, the signal strength in the first state becomes lower than the signal strength in the second state because the beam is absorbed.

For example, the detectormay be configured to extract a component (first component) of the output signal Sohaving a frequency twice the first frequency f. The first component changes according to the state of the first detection targetpresent on the path (first path) of the first beam B. The component of the frequency twice the first frequency fin the first state of the high concentration state is higher than the component of the frequency twice the first frequency fin thesecond state of the low concentration state.

For example, the detectormay be configured to extract a component (second component) of the output signal Sohaving a frequency twice the second frequency f. The second component changes according to the state of the second detection targetpresent on the path (second path) of the second beam B. The component of the frequency twice the second frequency fin a third state of the high concentration state is higher than the component of the frequency twice the second frequency fin a fourth state of the low concentration state. The concentration of the second detection target(such as the second gas) present on the path of the second beam Bin the third state is higher than the fourth concentration of the second detection targetpresent on the path in the fourth state.

is a schematic diagram illustrating the gas detection device according to the first embodiment.

illustrates the first beam Band the second beam B. The horizontal axis inis time tm. The vertical axis is the beam wavelength λ.

As shown in, the first wavelength λof the first beam Bchanges at the first frequency fbetween the first short wavelength λaand the first long wavelength λb. The first long wavelength λbis longer than the first short wavelength λa. The first intermediate wavelength λcexists between the first short wavelength λaand the first long wavelength λb.

As shown in, the second wavelength λof the second beam Bchanges at the second frequency fbetween the second short wavelength λaand the second long wavelength λb. The second long wavelength λbis longer than the second short wavelength λa. The second intermediate wavelength λcexists between the second short wavelength λaand the second long wavelength λb.

In one example, the second short wavelength λais longer than the first long wavelength λb. Alternatively, in the embodiment, the second long wavelength λbis shorter than the first short wavelength λa. In one example, the wavelengths of the first beam Band the second beam Bdo not substantially overlap. Thereby, the first detection targetcan be detected with higher accuracy by the first beam B. The second detection targetcan be detected with higher accuracy by the second beam B.

In the embodiment, the first beam Band the second beam Binclude near-infrared rays, mid-infrared rays, or far-infrared rays. The detection targetcan be detected with high accuracy.

For example, the first wavelength λmay be not less than 4.4 μm and not more than 4.7 μm. The second wavelength λmay be not less than 7.6 μm and not more than 7.9 μm.

As shown in, in the embodiment, the driver sectionmay include a signal generator. The signal generatoris configured to output a base signal Sbhaving a base frequency f. The drive signal may be controlled based on the base signal Sb. The operation of the detectormay be controlled based on the base signal Sb.

As shown in, in the embodiment, the driver sectionmay include a first multiplierand a second multiplierThe first multiplieris configured to supply the first driverwith a first signal Shaving a frequency that is a first integer multiple of the base frequency fbased on the base signal Sb. The first driversupplies the first laserwith the first drive signal Sdbased on the first signal S.

The second multiplieris configured to supply the second driverwith a second signal Shaving a frequency that is a second integer multiple of the base frequency fbased on the base signal Sb. The second driversupplies the second laserwith the second drive signal Sdbased on the second signal S. The second integer is different from the first integer. In this example, the first integer is 3. The second integer is 4. By using the base frequency fas a reference, the first laserand the second lasercan be controlled with high precision.

In the embodiment, the second frequency fmay be different from an integer multiple of twice the first frequency f. The first frequency fmay be different from an integer multiple of twice the second frequency f. Since the harmonics do not overlap, the output signal Socan be effectively separated.

In the embodiment, at least a part of the second period in which the second beam Bis emitted may overlap the first period in which the first beam Bis emitted. These beams may be emitted temporally overlapping each other. Detection with high accuracy is possible in a short time.

For example, a reference example may be considered in which beams of different wavelengths are emitted at different timings. In this reference example, the emission time of one beam per unit time is shortened. The beam intensity detection becomes low and it is difficult to obtain high accuracy. Alternatively, if sufficient intensity is obtained, the detection time becomes longer.

On the other hand, in the embodiment, at least a part of the plurality of beams having different wavelengths are emitted while temporally overlapping. Highly accurate detection is possible in a short time.

At least a part of the second beam Bmay spatially overlap with the first beam B. For example, even when the size of the sensoris small, the received beam Rcan be efficiently incident on the sensor. For example, high spatial resolution can be obtained.

As shown in, the gas detection devicemay further include a first optical elementThe first optical elementoverlaps the second beam Bwith the first beam B. In one example, the first optical elementmay be a low pass filter.

The received beam Rmay include reflected beams of the first beam Band the second beam B. As shown in, the first beam Band the second beam Bmay be reflected by the reflectorto become the received beam R. The reflectoris, for example, a retroreflector. The detection becomes easier. The gas detection devicemay include the reflector. The reflectormay be provided separately from the gas detection device. In the embodiment, the sensormay detect the first beam Band the second beam Bthat have passed through the space SPas the received beam R.

As shown in, the gas detection devicemay include a focus element. The focus elementcollects the beams (first beam B, second beam B, etc.) that have traveled through the space SP. Efficient detection becomes possible.

As shown in, the gas detection devicemay include a bandpass filter. The bandpass filtertransmits a part of the beam that has passed through the focus elementand attenuates other part. Unwanted signals are removed, making highly accurate detection easier. The beam that has passed through the bandpass filteris incident on the sensor.

As shown in, the gas detection devicemay include a preamplifier. Preamplifieramplifies the output signal Sofrom sensor. The output signal Sobeing amplified is supplied to the detector.

In one example, the detectormay include a lock-in amplifier. For example, as shown in, the base signal Sbhaving the base frequency f(or a signal corresponding to the base signal Sb) is supplied from the signal generatorto the detectoras a reference signal. In the detector, a target signal component is extracted using the base frequency for a frequency corresponding to the base frequency f. The extracted signal component becomes the detection result of the detection target.

As shown in, the gas detection devicemay include a controller. The controllermay include a processor, for example. The processoris configured to process the signal obtained from the detector(signal corresponding to the detection result). For example, the processormay compare the signal obtained from the detectorwith a reference value to determine the presence or absence of the detection target(gas). The determination result may be output.

The controllermay include a driver controller. The driver controlleris configured to control a plurality of drivers (such as the first driverand the second driver). For example, the first driversupplies the first drive signal Sdto the first laserbased on the output of the first multiplierand the control of the driver controller. For example, the second driversupplies the second drive signal Sdto the second laserbased on the output of the second multiplierand the control of the driver controller.

As shown in, the gas detection devicemay further include a visible light laser. The visible light laseremits a visible light beam B. For example, the visible light beam Bis emitted toward the space SPtogether with the first beam Band the second beam B. The visible light beam Bis used, for example, as a target laser.

As shown in, the driver sectionmay further include a third driver. The element sectionmay further include a third laser. The third laseris configured to be driven by the third driverand emit a third beam B. The third wavelength of the third beam Bchanges at a third frequency f. The third wavelength is different from the first wavelength λand different from the second wavelength λ. The third frequency fis different from the first frequency fand different from the second frequency f. The received beam Ris further based on the third beam B. The detectoris configured, for example, to further extract a third component of the output signal Sohaving a frequency twice the third frequency f.

As shown in, the gas detection devicemay further include a second optical elementThe second optical elementoverlaps the third beam Bwith the first beam B. In one example, the second optical elementmay be a low pass filter.